Electrographic printing or copying apparatuses are known; see for example WO 98/39691 A2 (U.S. Pat. No. 6,246,856 B1). In such a printing or copying apparatus, charge images of the images to be printed are generated by a character generator on a photoconductor element (for example a photoconductor belt or a photoconductor drum) charged to a charge potential by a charging unit via discharging to a discharge potential. The photoconductor element is subsequently moved past developer stations, respectively per color given color printing. These developer stations transport developer (comprised of toner and carrier, for example) to the photoconductor element. Toner transfers to the photoconductor element and inks this corresponding to the charge images on the photoconductor element. In color printing the toner images collected into a color image on a transfer belt are ultimately transfer-printed onto a printing substrate web and are fixed thereon. The precise workflow of the printing method can be learned from WO 98/39691 A2, the content of which is herewith incorporated into this disclosure.
FIG. 1 shows such a printing apparatus DR. A rotating photoconductor belt 3 as a photoconductor element is charged by a charging unit 2 (for example a corotron) to a charge potential. Charge images of the images to be printed are subsequently generated by a character generator 1 (for example an LED comb) on the photoconductor belt 3. For this the photoconductor belt 3 is discharged. The charge images are inked with toner into toner images via at least one developer station 6 with a developer roller. The individual toner images are transfer-printed onto, for example, a printing substrate web 7 at a transfer printing station 8. After the transfer printing, a residual toner remains on the photoconductor belt 3, which residual toner is initially recharged by a cleaning corotron 5 in order to then be cleaned off by a cleaning unit 4.
The cleaning unit 4 can, for example, have cleaning brushes 9 to remove the residual toner image from the surface of the photoconductor belt 3. The hairs of the cleaning brushes 9 lie at an electrical potential whose polarity is chosen so that the charged toner particles deposit on the brush hairs. The toner particles are thereby pushed from the surface of the photoconductor belt 3 by the mechanical brushing process in order to subsequently be able to electrostatically accumulate on the brush hairs. From a roller arrangement with a cleaning roller 10 that sweeps across the brush hairs of the cleaning brush 9 that have accumulated toner particles, the toner particles are again transferred via electrical fields from the brush hairs of the cleaning brush 9 to the cleaning roller 10 and are mechanically cleaned therefrom.
A method to operate an electrophotographic copying apparatus in which a cleaning of the photoconductor is conducted after the end of the copying operation is known from DT 25 57 622 A1. The photoconductor is thereby initially recharged in a pre-cleaning station. The photoconductor is then cleaned in a cleaning station with the aid of a triboelectrically charged brush.
DE 690 14 411 T2 describes an image generation apparatus that operates according to the electrophotographic principle. The apparatus has a cleaning device that recharges the residual toner on the photoconductor drum and subsequently cleans this by means of a brush.
The toner particles are slid across the photoconductor belt 3 by the mechanical detaching of the toner particles on the photoconductor belt 3 by the brush hairs of the cleaning brush 9, which has the result that the finest toner components accumulate on the surface of the photoconductor belt 3. This contamination grows over the course of the printing operation into a film on the surface of the photoconductor belt 3. The film interferes with the exposure of the surface of the photoconductor belt 3 and leads to disruption relevant to the print image.
To prevent the formation of the film on the surface of the photoconductor belt 3, a cleaning arrangement RA (for example with a gummy cleaning blade) is arranged on the surface of the photoconductor belt 3 in order to prevent the build-up of this film. Deposits of the smallest particles are removed from the photoconductor belt 3 by the cleaning arrangement RA before a growth of the film can be created.
The composition of the film is comprised of the smallest toner particles (for example silica) with a size of a few nanometers. These small particles are held on the surface of the photoconductor belt 3 with very strong adhesion forces. The electrical and mechanical forces of the brush hairs of the cleaning brush 9 are not sufficient to detach these particles from the surface of the photoconductor belt 3. This means that the cleaning arrangement RA must be pressed onto the surface of the photoconductor belt 3 with a correspondingly large force in order to capture and move the particles.
Since these particles (for example silica) are also very abrasive, the photoconductor belt 3 is slowly but continuously eroded during the cleaning. This has the result that the transport layer of the photoconductor 3 becomes increasingly thinner. Furthermore, the uniformity of the wear across the width of the photoconductor belt 3 becomes ever poorer with the increase of the wear. Two problems thereby occur that negatively affect the print quality:                The first problem results from the increasingly thinner transport layer of the photoconductor belt 3. The thinner that the transport layer of the photoconductor belt 3 becomes, the greater the danger of breakdowns of the charge applied to the photoconductor belt 3 to the metallization (reference ground) of the photoconductor belt 3. The breakdowns have the effect of small black points in the developed print image. Therefore the thickness of the photoconductor belt layer may not fall below a specific thickness.        The second problem results from the non-uniformity of the layer thickness across the width of the photoconductor belt 3. The charge that is applied with the corotron unit 2 to the transport layer of the photoconductor belt 3 is proportional to the layer thickness of the photoconductor belt 3. Thinner layer regions of the photoconductor belt 3 do not charge as strongly; to the contrary, thicker layer regions charge more strongly. The created charge regions on the photoconductor belt 3 are primarily recognizable as lighter and darker tracks in print rasters.        